Methods for exhausting a wafer coating apparatus

ABSTRACT

Methods for exhausting coating materials used in the process of spin coating a top surface of a wafer, the wafer having an edge and a bottom surface that is supported and rotated by a rotatable chuck attached by a shaft to a spin motor. The apparatus includes a bowl having an exhausted drain configured to receive excess liquid and vapor from the spin coating and an assembly configured to maintain the drain at a negative pressure differential relative to the bowl. In a preferred embodiment, a baffle is attached to the bottom to limit the flow of the liquid and vapor into the drain to a predetermined direction.

This application is a divisional application of U.S. patent applicationSer. No. 08/667,740, Filed Jun. 21, 1996, now U.S. Pat. No. 5,769,945.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to systems and methods forexhausting vapor and liquid. More particularly, the present inventionrelates to an exhaust system and method for a process bowl in a spincoating apparatus for the coating of wafer shaped semiconductormaterial.

2. Description of the Invention Background

Integrated circuits are typically constructed by depositing a series ofindividual layers of predetermined materials on a wafer shapedsemiconductor substrate, or "wafer". The individual layers of theintegrated circuit are in turn produced by a series of manufacturingsteps. For example, in forming an individual circuit layer on a wafercontaining a previously formed circuit layer, an oxide, such as silicondioxide, is deposited over the previously formed circuit layer toprovide an insulating layer for the circuit. A pattern for the nextcircuit layer is then formed on the wafer using a radiation alterablematerial, known as photoresist. Photoresist materials are generallycomposed of a mixture of organic resins, sensitizers and solvents.Sensitizers are compounds, such as diazonapthaquinones, that undergo achemical change upon exposure to radiant energy, such as visible andultraviolet light resulting in an irradiated material having differingsolvation characteristics with respect to various solvents than thenonirradiated material. Resins are used to provide mechanical strengthto the photoresist and the solvents serve to lower the viscosity of thephotoresist so that it can be uniformly applied to the surface of thewafers. After a photoresist layer is applied to the wafer surface, thesolvents are evaporated and the photoresist layer is hardened, usuallyby heat treating the wafer. The photoresist layer is then selectivelyirradiated by placing a radiation opaque mask containing a transparentportion defining the pattern for the next circuit layer over thephotoresist layer and then exposing the photoresist layer to radiation.The photoresist layer is then exposed to a chemical, known as developer,in which either the irradiated or the nonirradiated photoresist issoluble and the photoresist is removed in the pattern defined by themask, selectively exposing portions of the underlying insulating layer.The exposed portions of the insulating layer are then selectivelyremoved using an etchant-to expose corresponding sections of theunderlying circuit layer. The photoresist must be resistant to theetchant, so as to limit the attack of the etchant to only the exposedportions of the insulating layer. Alternatively, the exposed underlyinglayer(s) may be implanted with ions which do not penetrate thephotoresist layer thereby selectively penetrating only those portions ofthe underlying layer not covered by the photoresist. The remainingphotoresist is then stripped using either a solvent, or a strongoxidizer in the form of a liquid or a gas in the plasma state. The nextlayer is then deposited and the process is repeated until fabrication ofthe semiconductor device is complete.

Photoresist and developer materials are typically applied to the waferusing a spin coating technique in which the photoresist is dispensed onthe surface of the wafer as the wafer is spun on a rotating chuck. Thespinning of the wafer distributes the photoresist over the surface ofthe material and exerts a shearing force that separates the excessphotoresist from the wafer thereby providing a thin layer of photoresiston the surface of the wafer. Spin coating operations are performed in aclean room environment, and it is necessary to contain not only theexcess coating material that is separated from the wafer, but also thevapor resulting from the evaporation of the solvent. In addition,photoresist materials are generally very expensive, ranging from $500 to$2300/gallon, therefore, reducing the amount of coating material used inthe process can significantly reduce the overall cost of producingsemiconductor devices. Also, a build up of excess coating material inthe bowl requires additional downtime to remove and clean the bowl thatfurther increases production costs.

FIG. 1 shows a side view of a typical bowl 200 and a porous wafersupport chuck 202 of the prior art, such as is disclosed in U.S. Pat.No. 5,289,222 issued Feb. 22, 1994 to Hurtig. The wafer support chuck202 is supported by a shaft 204 that passes through a hole 206 in thebowl 200 and attaches to a spin motor 208 in a motor compartment 209. Awafer 210 having a top and a bottom surface, 212 and 214 respectively,is placed on the wafer support chuck 202 and is secured using a vacuum(not shown). The wafer 210 is spun and coating material, such asphotoresist or developer, is dispensed onto the top surface 212 of thewafer 210. The rotation of the wafer 210 causes the coating material todistribute over the top surface 212 and exerts a shear force on thecoating material that separates excess coating material from the surface212.

Some of the solvent in the excess coating material vaporizes uponleaving the surface producing dry aerosol particles of the coating mixedwith the liquid drops which accumulate over time on wall 216 of the bowl200. Also, the excess coating material has a tendency to creep aroundthe edge of the wafer 210 and contaminate the bottom surface 214. If thecoating material on the bottom surface 214 migrates to the chuck 202 aloss of vacuum could occur and the wafer 210 will be released, possiblydamaging the wafer. A solvent spray nozzle 218 is attached to the bowl200 and is directed toward the edge of the wafer 210 to rinse the bottomsurface 214, thereby preventing a buildup of coating material. Solventspray holes (not shown) are also provided in the bottom 217 of the bowl200 to rinse the coating solution from the bottom surface.

The excess liquid coating and liquid solvent are drained from the bowl200 using drain line 220 and the solvent vapors are purged from the bowl200 with air through air purge line 222. Solvent vapors are exhaustedfrom the motor compartment 209 through a safety exhaust line 224. Thedrain line 220, the air purge line 222 and the safety exhaust line 224are connected to an exhaust manifold and the vapor and liquid areseparated and either reclaimed or disposed accordingly.

One problem that exists with the prior art design shown in FIG. 1 isthat in the region between the bottom surface 214 of the wafer 210 andthe bottom of the bowl 217 a low pressure zone is created that resultsin a recirculation zone being formed that increases the amount ofcontamination that reaches the bottom surface 214 of the wafer 210, thebottom of the bowl 217, the chuck 202, and the motor 208. Therecirculation zone results in a lower production yield due tocontamination of the wafers and an increase in the overall processingtime due to the increased downtime required to clean the bowl 200.

One prior art effort to eliminate the recirculation zone, shown in FIG.2, employs a bowl 200 having a bottom 217 that is in close proximity tothe bottom surface 214. While this design does eliminate therecirculation zone beneath the bottom surface 214, the pressuredifferential between the edge of the wafer and the axis of rotation andthe proximity of the bottom 217 to the bottom surface 214 produces awicking effect that draws coating material in toward the center of thebowl 200. The proximity of the bottom surface 214 to the bottom 217 ofthe bowl 200 also makes it more difficult to rinse the coating materialoff the bottom surface 214 using the solvent spray nozzle 218.

Another problem is that prior art bowls are generally segregated, suchas by divider 226, to prevent the excess coating material from gettingsplashed or drawn onto the bottom surface 214 of the wafer 210. Whilethis design is effective for that purpose, the solvent is alsosegregated from the excess coating material that is removed from thewafer 210 and the dry aerosol particulates that are produced as thesolvent in the coating evaporates, all of which makes it more difficultto remove the liquid and solid coating material from the bowl 200. Theproblems of the liquid coating drying and forming a buildup occurs notonly in the bowl, but in the drain lines leading to the exhaustmanifold, which, of course, leads to increased downtime to clean thebowl and the drain lines. The amount of downtime required to clean thebowl in the prior art is further increased by the fact that in order tofully clean the bowl or the chuck and motor or to perform maintenance,the bowl and chuck have to be disassembled to separate the components.Thus, it is apparent that a need exists for an improved spin coatingbowl design which overcomes, among others, the above-discussed problemsso as to provide a spin coating bowl that requires less maintenance andthe maintenance that is performed requires less overall downtime.

SUMMARY OF THE INVENTION

The above objects and others are accomplished by a drain system andmethod in accordance with the present invention. The system is used inthe process of spin coating a top surface of a wafer with a coatingmaterial, the wafer having an edge and a bottom surface that issupported and rotated by a rotatable chuck attached by a shaft to a spinmotor. The drain system includes a bowl having an exhausted drainconfigured to receive excess liquid and vapor from the spin coating andan assembly configured to maintain the drain at a negative pressuredifferential relative to the bowl. In a preferred embodiment, a baffleis attached to the bottom to limit the flow of the liquid and vapor intothe drain to a predetermined direction.

Accordingly, the present invention provides an effective solution toproblems associated with the improper drainage of the process bowl so asto provide a cleaner process bowl, thereby reducing the extent ofdowntime required to clean the bowl. These and other details, objects,and advantages of the invention will become apparent as the followingdetailed description of the present preferred embodiment thereofproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the present invention will be described ingreater detail with reference to the accompanying drawings, wherein likemembers bear like reference numerals and wherein:

FIG. 1 is a side cross sectional view of a prior art spin coatingapparatus;

FIG. 2 is a side cross sectional view of another prior art spin coatingapparatus;

FIG. 3 is a side cross sectional view of a preferred embodiment of thepresent invention with a wafer supported by a chuck in a processposition;

FIG. 4 is a perspective cross sectional view of the bowl with the waferchuck disposed in the wafer loading position;

FIG. 5 is a side cross sectional view of the bowl with the wafer chuckdisposed in the maintenance position;

FIG. 6 is an exploded perspective view of the bowl with the air ring,top ring and baffle;

FIG. 7 is a top plan view of the air ring; and,

FIG. 8 is a side view of the exhausted drain attached to the bowl.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The operation of the apparatus 10 will be described generally withreference to the drawings for the purpose of illustrating presentpreferred embodiments of the invention only and not for purposes oflimiting the same. The apparatus 10 of the present invention includes aprocess bowl 12 through which a rotatable chuck 14 is disposed tosupport a wafer 16 having a diameter D, a top surface 13, a bottomsurface 15 and an edge 17 during a spin coating of a coating materialonto the wafer 16. The bowl 12 is attached to an exhausted drain system18 to allow for the removal of excess liquid and vapor coating materialspun off the wafer 16 during the spin coating operation, as well assolvent materials. While preferred embodiments of the invention will bediscussed with respect to spinning a coating material onto a circularsurface of a wafer, one skilled in the art will appreciate that theinvention can be suitably modified to dispense liquids onto any numberof surfaces.

In a preferred embodiment, the process bowl 12 is circularly shapedhaving a central axis A--A, and a bottom 20 and a side 22 defining aninterior region 24. The side 22 has an upper edge 21 with a vertical lip23 extending therefrom. The bottom 20 includes a generally cylindricallyshaped raised portion 26 surrounding central axis A--A having an uppersurface 25 containing a central opening 28 surrounded by an annularlower portion 27. The upper surface 25 of the raised portion 26 has aperipheral surface 32 that is sloped toward the lower portion 27 leadingto a circumferential step 34. Solvent dispense nozzles 30 are internallyformed in the raised portion 26 circumferentially around the centralaxis A-A and are attached to a solvent source (not shown) and directedat the bottom surface 15 of the wafer 16. The dispense nozzles 30 aredistributed circumferentially and are directed radially away from theaxis A--A through peripheral surface 32. The circumferential step 34contains notched leakage paths 36 corresponding to the location of thedispense nozzles 30 to allow solvent provided through the solventdispense nozzles 30 to drain to the lower annular portion 27. Theinterior region 24 is unsegregated or unpartitioned to facilitate theflow of excess liquid and vapor to the drain system 18. Alternatively,the interior region 24 could be partitioned to form segregated plenumand mutual fluid communication between the partitioned plenum and thedrain system 18 could be provided.

A circular air ring 40 is provided having an inner rim 42, an outer rim44 and top and bottom surfaces, 46 and 48, respectively. The top andbottom surfaces, 46 and 48, respectively, are crowned wherein the crownforms a circle having a diameter less than that of the wafer 16 anddefining an inner sloped surface 50 and an outer sloped surface 52. Theinner rim 42 is seated on the circumferential step 34 and the innersloped surface 50 and the sloped peripheral surface 32 define a firstcircumferential groove 54 having two edges, 55 and 56, respectively anda base 58. The solvent is dispensed using the dispense nozzle 30 and thesolvent and the excess coating material are directed toward the bottomsurface 15 of the wafer 16 above the groove 54 drained through thenotched leakage paths 36. Preferably a second circumferential groove 60is formed at the crown of the top surface 46 in close proximity to theedge 17 of the wafer 16, when the wafer 16 is supported by the chuck 14.The groove 60 is defined by edges, 56 and 62, respectively, and base 64contains perforations 66 extending from the top surface 46 through thebottom surface 48. The bottom surface 48 and the bottom 20 of the bowl12 define a lower plenum 70 that extends annularly around the raisedportion 26. The top surface 46 and the side 22 of the bowl 12 define anupper plenum 72 that extends annularly between the outer rim 44 of theair ring 40 and the side 22. When the inner rim 42 is seated on thecircumferential step 34, the outer rim 44 is preferably not in contactwith the bowl 12, thereby providing fluid communication between theupper and lower plenums, 70 and 72, respectively.

Preferably, a top ring 80 is provided having an inner lip 82 thatextends into the interior region 24 having a diameter greater than thediameter of the wafer 16 and an outer diameter containing twocircumferential steps 84 that mate with side edge 21 and lip 23. The topring 80 has a bottom face 86 that extends toward the bottom 20 of thebowl 12 and opposes the top surface 46 and preferably slopes from theinner lip 82 to the outer diameter, such that bottom face 86 is abovethe wafer 16 near the inner lip 82 and below the wafer 16 near the side22, when the wafer 16 is being supported in a process position, as shownin FIG. 3, and the bottom face 86 and the top surface 46 form a plenumregion that is part of the upper plenum 72. The bowl 12, air ring 40 andtop ring 80 are preferably constructed from a material that is resistantto, but wetted, by the spin coating chemicals and can be easily cleaned,such as Teflon®, although other material can be incorporated to suit theparticular needs of the practitioner.

In a preferred embodiment, the exhausted drain system 18 includes asingle drain 88 in the bottom 20 of the bowl 12, which is in closeproximity to the outer rim 44 and in fluid communication with the lowerand upper plenums 70 and 72, respectively, thereby providingunsegregated or unpartitioned access to the drain system 18. Theunsegregated access to the drain 88 reduces the amount of material thatprecipitates or drys in the bowl 12 resulting in fewer maintenanceshutdowns to clean the bowl. The use of a single drain provides forhigher flow rates near the drain which maintain particles in suspensionand leads to increased mixing of the solvent and the excess coatingmaterial allowing the coating material to be carried out of the system.Also, the use of a single drain and an unsegregated bowl maintains thesolvent vapors in contact with coating material preventing additionalevaporation of the solvent and drying of the coating material in thebowl 12 and in the drain lines. The exhausted drain 88 is connected toan exhaust manifold 90 through piping 92. The liquid and the vapor aregravitationally separated in the exhaust manifold 90 with the vaporexiting through exhaust pipe 96 and the liquid exiting through drain 98.A negative pressure is applied to the exhausted drain system 18 throughexhaust pipe 96, which draws vapor and liquid from the interior region24 of the bowl 12. A semicircular cylindrical baffle 100 is attached tothe bottom 20 around the drain 88 to more uniformly distribute the flowin the interior region 24. The presence of the exhausted drain 88 on oneside of the bowl 12 would tend to preferentially exhaust vapor from theportion of the bowl 12 nearest to the drain 88. The baffle 100 forcesthe vapor and liquid to flow into the drain 88 in a predetermineddirection resulting in a more uniform flow field in the interior region14 that further enhances the mixing of the solvent and the coatingmaterial providing for a cleaner bowl 12. In an alternative embodiment,the bottom 20 can be sloped to further aid the flow of the solvent andcoating material to the drain 88.

The drainage performance of the single drain 88 is enhanced through theuse of the chuck 14 that is dimensionally smaller than the opening 28 inthe bowl 12. The chuck 14 is disk shaped and attached by a shaft 102 toa spin motor (not shown) for rotation of the shaft 102 and the chuck 14and to servomotor (not shown), or other lift means, which is used toreciprocate the chuck 14 through the opening 28 between a maintenanceposition (FIG. 5), a process position (FIG. 3) and a wafer receivingposition (FIG. 4). Because the chuck 14 is dimensionally smaller thanthe opening 28, the processing position can be lowered with respect tothe raised portion 26 and the air ring 40, which allows the practitionerof the present invention to control the resistance of the flow path frombetween the wafer 16 and the raised portion 26 and the chuck 14 and theopening 28. An important aspect of controlling the resistance is thatthe flow of solvent vapors through the opening 28 can be minimized,because the path of least resistance will be through or around the airring 40 to the exhausted drain 88. Also, because the chuck 14 can bereciprocated through the opening 28, the spin motor and the servomotorcan be separated from the bowl 12, so that small amounts of solventvapor that may travel through the opening 28 can be processed with thesystem air all of which combine to eliminate the need to have adedicated vapor exhaust. In addition, the chuck 14 can be reciprocatedto its maintenance position and the bowl 12 or the chuck 14 and liftmeans can be maintained separately without the need to disassembleeither component, which greatly reduce maintenance time. For example, ifa process bowl 12 is to be cleaned, the chuck 14 can be lowered to themaintenance position and the process bowl 12 can be switched out andreplaced with another bowl so that the spin coating apparatus can beoperating while the cleaning is being performed which significantlyreduces the downtime of the processor. The chuck 14 is preferably a hardplastic, such as Teflon or polyphenylene sulfide (PPS), or a metal oxidethrough which a vacuum can be drawn using port 108 to secure the wafer16 on the chuck 14 and which also has a low thermal conductivity tominimize the amount of heat generated by the spin motor that istransferred to the wafer 16. In a preferred embodiment, the top surface104 has a circumferential raised rim 106 that allows the wafer 16 to besupported in sufficiently close proximity to the top surface 104 toallow the vacuum to hold the wafer 16, but the gap between the wafer 16and the top surface 104 further reduces the heat transfer to the wafer16.

In the operation and method of the present invention, the air ring 40 isinserted into the bowl 12 with the inner rim 42 seated on thecircumferential steps 84 and the top ring 80 is positioned so that thecircumferential steps 84 mates with side edge 21 and lip 23 on the side22 of the bowl 12. The chuck 14 is initially in the maintenance positionand then is moved through the process position to the wafer receiving,or loading, position using the servomotor. A wafer 16 is placed on thechuck 14 and a vacuum is drawn on the chuck 14 to secure the wafer 16and the chuck 14 is lowered to the process position. The spin motor isactivated to rotate the chuck 14 and wafer 16 and a negative pressure isapplied through the exhaust 96 as the coating material is then dispensedonto the wafer 16 using a dispense assembly connected to a coatingsource. The rotation of the wafer 16 causes the coating material todistribute over the top surface 13 of the wafer 16 and the majority ofthe excess coating material will be spun off the wafer 16 into the upperplenum 72 and will contact the downwardly sloping surfaces of either thetop surface 48 of the air ring 40, the side 22, or the bottom face 86,which serve to direct the flow of material toward the lower plenum 70and drain 88. Some of the excess coating material will creep around theedge 17 of the wafer 16 onto the bottom surface 15. The excess coatingmaterial will travel along the bottom surface 15 until it encounterscircumferential edge 62 which allows coating material to move downwardlyalong the surface 52 or toward base 64. If the material is not removedby edge 62, the excess coating material traveling toward axis A--A willnext encounter edge 56 which also allows the excess coating material toflow downwardly to base 64 or on surface 50, both of which are in fluidcommunication with the lower plenum 70. Excess coating material thatpasses edge 56 is sprayed by solvent nozzles 30, which are directed awayfrom axis A--A toward the bottom surface 15. The solvent and excesscoating material run down the downwardly sloping surfaces 50 and 32 andare drained through notched leakage paths 36 into the lower plenum 70.The proximity of the bottom surface 13 of the wafer 16 to the raisedportion 26 of the bowl 12 as a result of the chuck 14 having smallerdimension than the opening 28 serves to minimize the flow of solventback through the opening 28. The use of a single drain provides for anunsegregated exhaust system that allows the solvent to mix freely withthe excess coating material, thereby minimizing the amount of drycoating material that remains in the bowl 12 and the drain lines whenthe solvent evaporates. After the coating operation is complete, therotation of the wafer 16 and chuck 14 is stopped and the chuck is raisedusing the servomotor to the wafer receiving position and the wafer isremoved and another wafer is placed onto the chuck 14 or the chuck 14 islowered to the maintenance position, at which time the bowl 12 can beremoved for cleaning or maintenance can be performed on the chuck 14,spin motor and/or servomotor.

Those of ordinary skill in the art will appreciate that the presentinvention provides several advantages over the prior art. In particular,the subject invention eliminates the recirculation zone beneath thewafer and prevents capillary forces from being produced between the airring that can result in damage to the wafer by the inclusion of venteddepressions in the surface of the air ring. The subject invention alsoimproves the drainage of the process bowl so as to provide a cleanerprocess bowl, thereby reducing the extent of downtime required to cleanthe bowl. Also, the subject invention has the advantage of allowing thewafer chuck and motor assembly to be separated from the process bowlwithout disassembly of either component and provides added versatilityin the positioning of the wafer within the process bowl, which was notpresent in the prior art. While the subject invention provides these andother advantages over the prior art, it will be understood, however,that various changes in the details, materials and arrangements of partsand steps which have been herein described and illustrated in order toexplain the nature of the invention may be made by those skilled in theart within the principle and scope of the invention as expressed in theappended claims.

What is claimed is:
 1. A method of exhausting and draining excess liquidand vapor from a spin coating apparatus comprising:providing a bowlhaving an interior region; attaching an exhausted drain to the bowl soas to provide common access to the excess liquid and vapor in the bowl;deflecting substantially all of the excess liquid and vapor into theexhausted drain in a predetermined rotational direction; and applying anegative pressure to the exhausted drain.
 2. The method of claim 1wherein said deflecting comprises providing at least one baffle in thebowl.
 3. The method of claim 1 wherein said providing further comprisesproviding a bowl having an unpartitioned interior region.
 4. The methodof claim 1 wherein:said providing further comprises providing a bowlhaving a partitioned interior region; and said attaching furthercomprises attaching an exhausted drain to the bowl so as to providecommon access to the excess liquid and vapor in the bowl and fluidcommunication to the drain from the partitioned interior region.
 5. Amethod of coating a wafer, comprising:rotating the wafer within a bowl;dispensing a coating material on the wafer; applying a negative pressureto a single drain attached to the bowl; and deflecting substantially allflow of excess coating material and vapor from the bowl into the singledrain.
 6. The method of claim 5 wherein said deflecting furthercomprises orienting a baffle within the bowl to limit the flow of excesscoating within the bowl to a rotational direction that corresponds withsaid rotation of the wafer.
 7. A method of coating a wafer,comprising:rotating the wafer within a bowl; dispensing a coatingmaterial on the wafer; limiting flow of excess coating material andvapor within the bowl to a rotational direction that corresponds withsaid rotation of the wafer; applying a negative pressure tp a singledrain communicating with the bowl; and deflecting substantially all ofthe excess coating material and vapor from the bowl into the singledrain without retaining said excess coating material and vapor withinthe bowl.
 8. The method of claim 7 further comprising separating theexcess coating material and vapor.
 9. The method of claim 7 wherein saidlimiting further comprises orienting a baffle within the bowl to limitthe flow of excess coating material and vapor within the bowl to arotational direction that corresponds with the rotational direction ofthe wafer.
 10. A method of coating a wafer, comprising:rotating thewafer within a bowl having a bottom; dispensing a coating material onthe wafer; directing substantially all of a flow of excess coatingmaterial and vapor to the bottom of the bowl in a rotational directionthat corresponds with said rotation of the wafer; applying a negativepressure to a drain communicating with the bowl; and deflectingsubstantially all of the excess coating material and vapor from the bowlbottom into a single drain such that no pools of said excess coatingmaterial remain in the bowl after said deflecting.
 11. The method ofclaim 10 wherein said directing further comprises orienting a first ringwithin the bowl to direct the flow of excess coating material and vaporwithin the bowl to an area within the bowl wherein it can be drainedtherefrom.
 12. The method of claim 11 wherein said directing furthercomprises supporting a second ring within the bowl to cooperate with thefirst ring to define a passage within the bowl interior for directingthe flow of excess coating material and vapor within the bowl to an areawithin the bowl wherein it can be drained therefrom.
 13. The method ofclaim 12 wherein said directing further comprises orienting a bafflebetween a bottom surface of the bowl and the first ring to limit theflow of excess coating and vapor within the bowl to a rotationaldirection that corresponds with said rotation of the wafer and to directthe excess coating material and vapor to a drain in the bottom of thebowl.
 14. A method of coating a wafer, comprising:rotating the waferwithin a bowl having a bottom; dispensing a coating material on thewafer; orienting a first ring within the bowl; supporting a second ringwithin the bowl to cooperate with the first ring to direct substantiallyall excess coating material and vapor within the bowl to an area whereinit can be drained from the bowl; orienting a baffle between the bottomof the bowl and the first ring to limit the flow of excess coating andvapor within the bowl to a rotational direction that corresponds withthe rotational direction of the wafer and to deflect the excess coatingmaterial and vapor to a single negatively pressurized drain in thebottom of the bowl; deflecting substantially all of the excess coatingmaterial and vapor from the bowl bottom; and separating the excesscoating material and vapor drained from the bowl.
 15. A method ofexhausting a bowl that has an interior wherein a wafer is rotated andcoated with a coating material, said method comprising:limiting flow ofexcess coating material and vapor within the bowl interior to arotational direction that corresponds with said rotation of the wafer;and deflecting substantially all of the excess coating material andvapor from the bowl interior into a single negatively pressurized drainsuch that the bowl is substantially free from excess coating materialand vapor upon completion of said deflecting.
 16. The method of claim 15wherein said limiting further comprises orienting a baffle within thebowl to limit the flow of excess coating and vapor within the bowlinterior to a rotational direction that corresponds with the rotationaldirection of the wafer.
 17. The method of claim 15 wherein the bowl hasa bottom and said deflecting further comprises attaching a drain conduitto the bowl bottom.
 18. The method of claim 15 further comprisingseparating the excess coating material and vapor.
 19. A method ofexhausting a bowl that has a bottom and a side that defines an interiorwherein a wafer is rotated and coated with a coating material, saidmethod comprising:directing substantially all excess coating material tothe bottom of the bowl in a rotational direction that corresponds withsaid rotation of the wafer; negatively pressurizing a single draincommunicating with the bowl; and deflecting substantially all of theexcess coating material and vapor from the bowl bottom into the singledrain.
 20. The method of claim 19 wherein said directing furthercomprises orienting a first ring within the bowl to direct the excesscoating material and vapor within the bowl to an area wherein it can bedrained therefrom.
 21. The method of claim 20 wherein said directingfurther comprises supporting a second ring within the bowl to cooperatewith the first ring to define a passage within the bowl interior fordirecting the excess coating material and vapor within the bowl to anarea within the bowl wherein it can be drained therefrom.
 22. The methodof claim 20 wherein said directing further comprises orienting a bafflebetween the bottom of the bowl and the first ring to limit the flow ofexcess coating and vapor within the bowl interior to a rotationaldirection that corresponds with the rotational direction of the waterand to deflect the excess coating material and vapor to the singledrain.
 23. A method of exhausting a bowl that has a bottom and a sidethat defines an interior wherein a wafer is rotated and coated with acoating material, said method comprising:orienting a first ring withinthe bowl; supporting a second ring within the bowl to cooperate withsaid first ring to define a passage within the bowl interior fordirecting substantially all excess coating material and vapor within thebowl to an area within the bowl wherein it can be drained therefrom;orienting a baffle between the bottom of the bowl and the first ring todeflect the flow of substantially all of the excess coating material andvapor within the bowl to a rotational direction that corresponds withthe rotational direction of the wafer and to direct substantially all ofthe excess coating material and vapor to a single negatively pressurizeddrain in the bottom of the bowl; and separating substantially all of theexcess coating and vapor drained from the bowl.